四川盆地下寒武统筇竹寺组海相页岩气高产井突破与富集模式

Breakthrough and enrichment mode of marine shale gas in the Lower Cambrian Qiongzhusi Formation in high-yield wells in Sichuan Basin

多年来下寒武统筇竹寺组页岩气勘探开发进展缓慢,资201井获高产气流大大增加了该套页岩气规模商业化开发的信心,不同区域及层段富集规律差异及下一步勘探开发方向是筇竹寺组页岩开发面临的首要问题。以四川盆地57口钻井资料为基础,对多口重点井的古生物、沉积、储层等特征进行分析,详细剖析资201井的部署理论依据、筇竹寺组页岩气富集条件及下一步勘探开发方向。从地层研究入手,建立了筇竹寺组地层划分标准,明确筇竹寺组主体发育4套深水陆棚相的富有机质页岩(①至④号层段),其分布受裂陷槽发育控制,裂陷槽内厚度最大。分析了页岩储层发育特征,指出储层压力、孔隙度、含气饱和度从下向上、从裂陷槽外到内呈现增大趋势,储层超压对页岩孔隙保存起到重要作用;基于此结合保存条件等建立了“多层异相、超压保孔”的页岩气超压差异富集模式,指出远离散失通道的超压孔隙发育区(层段)是页岩气富集有利区(层段)。文章指出资201井及周边是未来筇竹寺组页岩气增储上产的主要区域,资源量为8.06×10^(12)m^(3);川西地区具有相当的开发潜力,资源量为0.72×10^(12)m^(3);川南长宁及黔北一带受石墨化及构造活动影响,以寻找远离风化壳及地表露头的超压孔隙发育区为主。

Small progress has been made in the exploration and development of shale gas in the Lower Cambrian Qiongzhusi Formation over the years.The high-yield gas flow in Well Zi 201 has greatly increased confidence in the large-scale and commercial development of shale gas in Qiongzhusi Formation.The different enrichment laws in various areas and layers and the optimal selection of favorable areas are the primary problems to be solved for shale gas development.Based on the analysis of paleontology,sedimentary facies,and reservoirs in 57 wells in Sichuan Basin,the theoretical basis for the deployment of Well Zi 201 and enrichment conditions of shale gas in Qiongzhusi Formation are analyzed in detail,and the exploration and development orientation are pointed out.Firstly,a stratification standard for Qiongzhusi Formation is established.It is clarified that four sets of organic rich shale of deep shelf facies were developed in Qiongzhusi Formation(layers①,②,③,and④),which were controlled by the development of rift troughs,with the largest shale thickness in the trough.The characteristics of shale reservoirs are analyzed,which indicate that the reservoir pressure,porosity,and gas saturation show an increasing trend from bottom to top,and from the outside to the inside of the rift trough,and reservoir overpressure plays an important role in the preservation of shale pores.On this basis,an overpressure and differential shale gas enrichment mode of“different facies in multiple layers and overpressure pore preservation”in Qiongzhusi Formation has been established,and it is pointed out that the overpressure pore development area(interval)far away from the dispersion pathway is the favorable area(interval)for shale gas enrichment.Finally,the study results indicate that Well Zi 201 and its surrounding areas are the main areas for increasing shale gas reserves and production in the future,with resources of 8.06×10^(12)m^(3).It shows considerable development potential in western Sichuan Basin,with resources of 0.72×10^(12)m^(3).Affected by graphitization and tectonic activities,areas with overpressure pore development far from weathered crust and surface outcrops are favorable for shale gas exploration in Changning in southern Sichuan Basin and northern Guizhou Province.